Atherosclerosis of the carotid arteries is a common cause of stroke. The prevalence and progression of carotid atherosclerosis are believed to be influenced by genetically inherited variations in lipoprotein metabolism. This study investigates the specific role of paraoxonase, an enzyme thought to detoxify atherogenic oxidized low-density lipoprotein. This study compares veterans who have significant carotid atherosclerosis on ultrasound examination with controls without carotid atherosclerosis. Both paraoxonase activity and genotype will be determined and compared between groups. The results may eventually make it possible to screen for a paraoxonase allele that confers high risk of atherosclerosis, and to diminish the risk by early treatment.